Method of detecting FSK-modulated signals, corresponding circuit, device and computer program product

ABSTRACT

An occurrence of a first set of n periods of a frequency-shift-keying (FSK)-modulated waveform is counted, where n is an integer number. The n periods of the FSK-modulated waveform in the first set have a first time duration. An occurrence of a second set of n periods of the waveform is counted. The n periods of the waveform in the second set have a second time duration. The first time duration is determined based on the counting of the first set of n periods. The second time duration is determined based on the counting of the second set of n periods. A difference between the first time duration and the second time duration is compared to a threshold. Changes in frequency of the waveform are detected based on the comparing of the difference between the first time duration and the second time duration to the threshold.

BACKGROUND Technical Field

The description relates to detecting FSK-modulated signals.

One or more embodiments may be applied to arrangements where informationis exchanged between two devices. A “charger” device and a “charged”device exchanging information in order to regulate/adjust a chargingprocess in, e.g., a wireless charger may be exemplary of such anarrangement.

Description of the Related Art

Frequency modulation (FM) involves a variation of the frequency of amodulated signal as a function of a modulating signal, such as, e.g., aninformation-carrying data signal.

A common type of frequency modulation is Frequency Shift Keying (FSK).For instance, in two-level FSK (2-FSK) two different frequencies maycorrespond to two different binary levels (e.g., “0” and “1”).

The frequency spectrum of the corresponding modulated signal includes aplurality of lines at locations dictated by the deviation frequency Δfand the modulation speed fc, as expressed e.g., in bauds.

Various types of circuits may be used for demodulating an FSK-modulatedsignal.

A basic detection approach may rely on the detection of passages throughzero (zero-crossings) of the modulated signal.

A corresponding circuit may include a (baseband) filter, a thresholdoperational amplifier, a derivative block, a rectifier diode, amonostable circuit, a low-pass filter and a Schmitt Trigger. In such anarrangement, the received signal is passed through a band-pass filter toremove out-of-band noise. The filtered signal is fed to a thresholdcomparator that detects the number of zero crossings. The derivativeblock and a rectifier (e.g., a diode) may generate positive spikes atthe rising edges of the square wave signal output from the comparator. Amonostable circuit may then generate constant duration pulses at theinstances where the spikes occur. The pulses so generated are thenlow-pass filtered and passed on to a trigger circuit which is configuredto detect the received signal as “1” or “0” according to whether thelow-pass filtered signal is, e.g., above and below, respectively, adetection threshold.

Correct demodulation is facilitated by the absence of phase “jumps” inthe FSK signal when passing from one frequency to another: such jumpsmay in fact militate against determining the exact moment wherevariation of the modulated signal occurred.

An alternative detection method may include using a processing devicesuch as, e.g., a DSP core, which may compute the frequency of theFSK-modulated signal (e.g., via DFT calculation or the like), followedby filtering to remove noise; frequency variations are then evaluated inorder to detect the information-carrying signal.

Arrangements as discussed in the foregoing may suffer from variousdisadvantages including, e.g., circuit complexity (also in terms of asilicon area in the case of integrated circuits) and cost and exhibit anintrinsic weakness with respect to phase-variations (“jumps”) whentransitioning from a frequency to another.

Documents such as U.S. Pat. No. 9,225,568 B1 suggest using a counter fortiming a fixed number of FSK-cycles. The frequency of the receivedsignal may then be determined by comparing the count values with adetermined threshold. Comparing the received number with an expectednumber makes it possible to discriminate between, e.g., two modulationfrequencies f0 and f1.

BRIEF SUMMARY

Despite the extensive activity in that area, improvement may be desired,e.g., as regards one or more of the following:

-   -   robustness against phase jumps and possible frequency drifts,        e.g., in the carrier signal which is FSK-modulated;    -   the capability of operating in a MFSK (Multiple Frequency-Shift        Key) scenario, involving multi-level modulating signals (e.g.,        4-FSK, 8-FSK, . . . ); and/or    -   the capability of operating with different communication        standards, such as, by way of example, the Qi 1.2 communication        protocol and the PMA communication protocol.

In an embodiment, a method of detecting a FSK-modulated waveform whereinthe period of the FSK-modulated waveform varies as a function of thelevel of a digital modulating signal, comprises: counting the occurrenceof a first set of n periods of the FSK-modulated waveform, said nperiods of said FSK-modulated waveform in said first set having a firsttime duration, counting the occurrence of a second set of n periods ofsaid FSK-modulated waveform, said n periods of said FSK-modulatedwaveform in said second set having a second time duration, detecting andcomparing said first time duration and said second time duration, anddetecting a change in the frequency of said FSK-modulated waveformindicative of a change in the level of said digital modulating signal asa result of said comparison indicating a difference between said firsttime duration and said second time duration reaching a detectionthreshold. In an embodiment, said first set of n periods and said secondset of n periods are neighboring sets of periods in said FSK-modulatedwaveform. In an embodiment, the method includes cyclically counting theoccurrence of sets of n periods of said FSK-modulated waveform oversubsequent time windows wherein: said first set of n periods includes aset of n periods of said FSK-modulated waveform during a current timewindow, and said second set of n periods includes a set of n periods ofsaid FSK-modulated waveform during a previous time window. In anembodiment, the method includes making said number n of periods of saidFSK-modulated waveform selectively adjustable. In an embodiment, themethod includes making said difference threshold selectively adjustable.In an embodiment, the method includes recovering said digital modulatingsignal as a function of the changes in the frequency of saidFSK-modulated waveform detected as a result of said comparison. In anembodiment, the method includes buffering the information bits conveyedby said recovered digital modulating signal. In an embodiment, themethod includes generating interrupt signals for at least partlydiscontinuing detection as a result of reception of said FSK-modulatedwaveform being discontinued. In an embodiment, the method includesgenerating interrupt signals for at least partly discontinuing detectionas result of one of: the number of said buffered bits reaching athreshold value, the buffered bits having filled a respective buffer.

In an embodiment, a circuit comprises: counting circuitry configured tocount the occurrence of sets of n periods in a FSK-modulated waveform,wherein the period of said FSK-modulated waveform varies as a functionof the level of a digital modulating signal, the counting circuitry isconfigured to: i) count the occurrence of a first set of n periods ofsaid FSK-modulated waveform, said n periods of said FSK-modulatedwaveform in said first set having a first time duration, ii) count theoccurrence of a second set of n periods of said FSK-modulated waveform,said n periods of said FSK-modulated waveform in said second set havinga second time duration, a frequency change detection circuit coupledwith said counting circuitry to receive therefrom at least one signalindicative of said first time duration and said second time duration,comparing said first time duration and said second time duration andgenerating at least one detection signal indicative of the occurrence ofvariations in the frequency of said FSK-modulated waveform as a resultof the difference between said first time duration and said second timeduration reaching a detection threshold. In an embodiment, the circuitis an FSK-demodulator including a bit decoder coupled with said circuitto receive therefrom said at least one detection signal indicative ofthe occurrence of variations in the frequency of said FSK-modulatedwaveform, the bit decoder configured to recover from said at least onedetection signal the information bits conveyed by said digitalmodulating signal. In an embodiment, the FSK-demodulator includes abuffer to store a plurality of information bits conveyed by said digitalmodulating signal recovered from said at least one detection signal. Inan embodiment, said decoder is configured to decode at least one of adifferential by-phase encoded signal and a Manchester-encoded signal.

In an embodiment, a method comprises: counting an occurrence of a firstset of n periods of a frequency-shift-keying (FSK)-modulated waveform,where n is an integer number, said n periods of said FSK-modulatedwaveform in said first set having a first time duration, wherein aperiod of the FSK-modulated waveform varies as a function of a level ofa digital modulation signal; counting an occurrence of a second set of nperiods of said FSK-modulated waveform, said n periods of saidFSK-modulated waveform in said second set having a second time duration;determining, based on the counting of the first set of n periods, thefirst time duration; determining, based on the counting of the secondset of n periods, the second time duration; comparing a differencebetween said first time duration and said second time duration to athreshold; and detecting a change in a frequency of said FSK-modulatedwaveform indicative of a change in the level of said digital modulatingsignal based on the comparing of the difference between the first timeduration and the second time duration to the threshold. In anembodiment, said first set of n periods and said second set of n periodsare neighboring sets of periods in said FSK-modulated waveform. In anembodiment, the method comprises: cyclically counting occurrences ofsets of n periods of said FSK-modulated waveform over sequential timewindows wherein: said first set of n periods includes a set of n periodsof said FSK-modulated waveform during a current time window, and saidsecond set of n periods includes a set of n periods of saidFSK-modulated waveform during a previous time window. In an embodiment,the method comprises: adjusting said number n of periods of saidFSK-modulated waveform. In an embodiment, the method comprises:adjusting said threshold. In an embodiment, the method comprises:recovering said digital modulation signal as a function of detectedchanges in the frequency of said FSK-modulated waveform based on aseries of comparisons of differences between durations of sets of nperiods to the threshold. In an embodiment, the method comprises:buffering information bits of said recovered digital modulation signal.In an embodiment, the method comprises: detecting a discontinuation ofreception of the FSK-modulated waveform; and generating an interruptsignal in response to the detection of the discontinuation. In anembodiment, the method comprises: generating an interrupt signal inresponse to at least one of: a number of said buffered bits reaching athreshold number of bits; and a buffer overflow.

In an embodiment, a device comprises: one or more memories; andfrequency-shift detection circuitry, which, in operation: countsoccurrences of sets of n periods of a received frequency-shift-keying(FSK)-modulated waveform, where n is an integer number; determines,based on the counting, time durations corresponding to respective setsof n periods; compares differences between time durations correspondingto respective sets of n periods to a threshold difference; and generatesone or more signals indicative of variations in frequency of theFSK-modulated waveform based on the comparing of the differences betweentime durations to the threshold difference. In an embodiment, thefrequency-shift detecting circuitry, in operation, compares differencesbetween time durations of neighboring sets of n periods in saidFSK-modulated waveform to the threshold difference. In an embodiment,the frequency-shift detecting circuitry, in operation: cyclically countsoccurrences of sets of n periods of said FSK-modulated waveform oversequential time windows wherein: a first set of n periods includes a setof n periods of said FSK-modulated waveform during a current timewindow; a second set of n periods includes a set of n periods of saidFSK-modulated waveform during a previous time window; and a differencebetween a time duration corresponding to the first set of n periods anda time duration corresponding to the second set of n periods is comparedto the threshold difference. In an embodiment, n is adjustable. In anembodiment, the threshold difference is adjustable. In an embodiment,the device comprises: decoding circuitry, which, in operation, recoversa digital modulation signal based on the one or more signals indicativeof variations in frequency of the FSK-modulated waveform generated inresponse to a series of comparisons of differences between durationscorresponding to sets of n periods to the threshold difference. In anembodiment, wherein the frequency-shift detecting circuitry, inoperation, recovers a digital modulation signal based on the one or moresignals indicative of variations in frequency of the FSK-modulatedwaveform generated in response to a series of comparisons of differencesbetween durations corresponding to sets of n periods to the thresholddifference. In an embodiment, the one or more memories comprise abuffer, which, in operation, buffers information bits of said recovereddigital modulation signal. In an embodiment, the frequency-shiftdetecting circuitry, in operation: detects discontinuations of receptionof the FSK-modulated waveform; and generates an interrupt signal inresponse to detection of a discontinuation. In an embodiment, thefrequency-shift detecting circuitry, in operation, generates aninterrupt signal in response to at least one of: a number of saidbuffered bits reaching a threshold number of bits; and a bufferoverflow.

In an embodiment, a system comprises: receiving circuitry, which, inoperation: counts occurrences of sets of n periods of a receivedfrequency-shift-keying (FSK)-modulated waveform, where n is an integernumber; determines, based on the counting, time durations correspondingto respective sets of n periods; compares differences between timedurations corresponding to respective sets of n periods to a thresholddifference; and generates one or more signals indicative of variationsin frequency of the FSK-modulated waveform based on the comparing of thedifferences between time durations to the threshold difference; anddecoding circuitry, which, in operation, recovers a digital modulationsignal based on the one or more signals indicative of variations infrequency of the FSK-modulated waveform generated in response to aseries of comparisons of differences between durations corresponding tosets of n periods to the threshold difference. In an embodiment, thesystem includes a buffer, which, in operation, stores information bitsof the recovered digital modulation signal. In an embodiment, thedecoding circuitry, in operation, decodes at least one of a differentialby-phase encoded signal and a Manchester-encoded signal. In anembodiment, the system comprises: power control circuitry, which, inoperation, controls a charging process based on the recovered digitalmodulation signal.

In an embodiment, a non-transitory, computer-readable medium's contentscause a signal processing circuit to perform a method, the methodcomprising: counting occurrences of sets of n periods of a receivedfrequency-shift-keying (FSK)-modulated waveform, where n is an integernumber; determining, based on the counting, time durations correspondingto respective sets of n periods; comparing differences between timedurations corresponding to respective sets of n periods to a thresholddifference; and generating one or more signals indicative of variationsin frequency of the FSK-modulated waveform based on the comparing of thedifferences between time durations to the threshold difference. In anembodiment, the method comprises: recovering a digital modulation signalbased on the one or more signals indicative of variations in frequencyof the FSK-modulated waveform generated in response to a series ofcomparisons of differences between durations corresponding to sets of nperiods to the threshold difference. In an embodiment, the methodcomprises: controlling a charging process based on the recovered digitalmodulation signal. In an embodiment, the signal processing circuitcomprises one or more memories and one or more processing cores.

One or more embodiments may relate to a method as disclosed herein, acorresponding circuit (e.g., a FSK detector), a corresponding device(e.g., a FSK demodulator) and a corresponding computer program productloadable into the memory of at least one processing device and includingsoftware code portions for executing a method as disclosed herein whenthe product is run on at least one processing device. As used herein,reference to such a computer program product is understood as beingequivalent to reference to a computer-readable medium containinginstructions for controlling the processing system in order toco-ordinate implementation of the method according to one or moreembodiments. Reference to “at least one processor device” is intended tohighlight the possibility for one or more embodiments to be implementedin modular and/or distributed form.

One or more embodiments may involve detecting the difference between twofrequencies used for modulation, e.g., the difference between afrequency currently detected and a frequency previously detected.

Consequently, operation of one or more embodiments may not be directlylinked to the (absolute value of) the frequencies used, whichfacilitates decoding a modulating signal also in an MFSK scenario.

One or more embodiments may exhibit an intrinsic robustness againstfrequency shifts and/or phase jumps.

One or more embodiments may operate effectively in connection with,e.g., transmission protocols involving a sort of differential operation,e.g., where the frequency generated during a certain time interval islinked to the frequency generated in a previous time interval, so thatthe information to be detected lies in the difference between these twofrequencies and not in the sequence of the absolute frequency valueswhich are transmitted/received.

One or more embodiments may facilitate detecting a Qi signal (which isdifferentially encoded by using a bi-phase system), as well as a PMAsignal based on the use of a Manchester code.

In contrast with conventional approaches for detection of FSK-modulatedsignals (wherein the—absolute—values of the frequencies received areestimated and a corresponding bit sequence re-constructed on the basisof the sequence of the frequencies received and the modulation rule,applied in a complementary way with respect to the modulator) one ormore embodiments may re-construct the sequence of the bits conveyed inthe digital modulated signal directly, namely by exploiting thefrequency transitions, which by themselves already include the binaryinformation transmitted in so far as this is applied differentially.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more embodiments will now be described, by way of example only,with reference to the annexed figures, wherein:

FIG. 1, including two portions indicated a) and b) respectively, isexemplary of FSK-modulation,

FIG. 2 is a schematic representation of an embodiment of a detectionwindow to detect a frequency change in an FSK-modulated signal,

FIG. 3 is a general functional block diagram exemplary of one or moreembodiments of an FSK demodulator,

FIG. 4 is a block diagram of one or more embodiments,

FIG. 5 is a block diagram exemplary of possible features of one or moreembodiments, and

FIG. 6 is a flow chart exemplary of possible operation of embodiments.

DETAILED DESCRIPTION

In the ensuing description, one or more specific details areillustrated, aimed at providing an in-depth understanding of examples ofembodiments of this description. The embodiments may be obtained withoutone or more of the specific details, or with other methods, components,materials, etc. In other cases, known structures, materials, oroperations are not illustrated or described in detail so that certainaspects of embodiments will not be obscured.

Reference to “an embodiment” or “one embodiment” in the framework of thepresent description is intended to indicate that a particularconfiguration, structure, or characteristic described in relation to theembodiment is included in at least one embodiment. Hence, phrases suchas “in an embodiment” or “in one embodiment” that may be present in oneor more points of the present description do not necessarily refer toone and the same embodiment. Moreover, particular conformations,structures, or characteristics may be combined in any adequate way inone or more embodiments.

The references used herein are provided merely for convenience and hencedo not define the extent of protection or the scope of the embodiments.

The upper portion, designated a), of FIG. 1 is exemplary of the possibletime behavior of a (sinusoidal) signal which is FSK-modulated as afunction of a digital modulating signal having the time behaviorexemplified in the lower portion, designated b), of FIG. 1.

Specifically, FIG. 1 is exemplary—in a non-limiting sense of theembodiments—of two-level FSK-modulation (2-FSK) wherein the frequency ofthe FSK-modulated signal (portion a)) is switched between a “low” valuef0 and a “high” value f1 as a function of the logical value of themodulating signal (portion b) switching between “0” and “1”.

In both portions of FIG. 1, the abscissa scale indicates time, and theordinate scale indicates the amplitude A (in arbitrary units).

For instance, while the representation of FIG. 1 assumes that:

-   -   a transition from frequency f0 to frequency f1 in the        FSK-modulated signal corresponds to a transition from “0” to “1”        in the (digital) modulating signal, and    -   a transition from frequency f1 to frequency f0 in the        FSK-modulated signal corresponds to a transition from “1” to “0”        in the modulating signal,

the opposite may apply.

Similarly, FSK-modulation may involve using more than two frequencies,e.g., f0, f1, f2, f3, thus permitting multi-level modulation, e.g.,“00”→f0, “01”→f1, “10”→f2, “11”→f3 in the case of 4-FSK.

The foregoing corresponds to well-known principles in signal theory,thus making it unnecessary to provide a more detailed descriptionherein.

The representation of FIG. 1 is thus generally exemplary of anFSK-modulated waveform, wherein the frequency (that is, the period) ofthe modulated waveform varies as a function of the level of a digitalmodulating signal.

FIG. 2 is exemplary of a possible criteria for detecting anFSK-modulated signal (see, e.g., the upper portion a) in FIG. 1) asrepresented as a function of frequency (abscissa scale).

An area (Dzone area) may be defined around a currently receivedfrequency Ffsk representative of a window of a width 2×D (e.g., between−D and +D around Ffsk), such that reception of frequency outside thewindow in question (a window symmetrical around Ffsk is exemplified forthe sake of simplicity, this feature being otherwise non limiting) maybe held to correspond to a change in frequency of the FSK-modulatedwaveform indicative of a level change (e.g., “0”→“1” or “1”→“0”) in themodulating signal which is to be recovered at the detector side.

The block diagram of FIG. 3 is exemplary of a possible arrangement of anFSK-demodulator 10 according to one or more embodiments.

For instance, in one or more embodiments, an FSK-modulated incomingsignal FSK_(in) (see, e.g., portion a) of FIG. 1) may be fed into afrequency change detection block 12 where the FSK-modulated signalFSK_(in) is analyzed to detect a change in its frequency.

The detected signal output from the frequency change detection block 12may be fed to a bit decoding block 14 (including, e.g., a Finite StateMachine—FSM) to evaluate subsequent frequency changes (e.g., positive ornegative +/− between two frequencies f0 and f1) and decode themodulating signal (e.g., bits “0” and “1”, by referring to the examplein the lower portion of FIG. 1) in order to produce a decoded receivedbit sequence (e.g., . . . 1, 0, 1, 0, 1, . . . ).

In one or more embodiments, the decoded bits may be stored in a buffer16 with a view to producing an output signal OUT for use in a devicecoupled to the FSK-demodulator 10. A charger/charged device asexemplified in the introductory portion of the description may beexemplary of such use or devices.

It will be otherwise understood that the representation of FIG. 3 ismerely exemplary in so far as, e.g., in one or more embodiments thebuffer 16 may be dispensed with.

A FSK-demodulator as exemplified in FIG. 3 may be used for demodulatinga variety of FSK-modulated signals, such as, e.g., signals encodedaccording to the Qi or PMA protocols already mentioned.

One or more embodiments, as exemplified in FIG. 3 may becontrolled/programmed, e.g., by means of an external processing unit,such as a microprocessor unit or MPU.

For instance, in one or more embodiments the possibility may exist ofgenerating interrupts for such a unit every time a change in thefrequency of the incoming signal FSK_(in) occurs (by leaving the relatedprocessing to software-based modules).

In one or more embodiments the possibility may exist of receiving, e.g.,Qi or PMA data and issue an interrupt to the processing unit (e.g.,only) when a certain number of bits have been received.

In one or more embodiments, the processor may store in its configurationregisters a type of demodulation as required, the number of receivedbits to be stored in the buffer and other possible parameters involvedin a decoding algorithm (which may be then performed, e.g., via hardwareIPs).

It will be appreciated that one or more embodiments may be able todecode signals in compliance with protocols such as Qi/PMA by operating(e.g., solely) on the output of the frequency change detector 12 whichdetects frequency variations.

As illustrated, the FSK demodulator 10 of FIG. 3 includes one or moreprocessors P, one or more memories M and one or more discrete circuitsDC, which may be used alone or in various combinations to implement thefunctions of the FSK demodulator 10.

The block diagram of FIG. 4 is exemplary of a possible layout of anembodiment of the FSK demodulator circuit 12 of FIG. 3 and its possiblecooperation with the bit decoder circuit 14.

FIG. 4 also shows the possible presence, in one or more embodiments, ofan (e.g., external) processing unit 120 such as, e.g., a microprocessorunit or controller (MPU) as discussed in the foregoing with associatedconfiguration registers 122. The controller 120 may, for example,control a power charging process or other processes based on a decodedsignal.

In FIG. 4, reference 124 denotes an “event” counter module or circuitreceiving as an input the FSK-modulated signal FSK_(in) and a frequencychange signal FC and producing an event number signal EN. Such an eventcounter 124 may be included in one or more embodiments in order to countthe number of pulses/waveforms of the modulated input signal FSK_(in)between two frequency changes. In one or more embodiments such lengthinformation may be exploited in order to facilitate correct demodulationof the received bits as discussed in the following.

In FIG. 4, reference 125 denotes a “window” counter module or circuitwhich may be driven by the controller 120 (e.g., via the registers 122)and which may receive as an input the FSK-modulated signal FSK_(in), awindow size signal WS (possibly provided by the processing unit orcontroller 120) and produce a start and stop signal to a counter 126.

In one or more embodiments, the counter 126 may be a free runningcounter clocked by an input clock signal clk, coupled with the windowcounter 125 and configured for (cyclically) issuing input signalsindicative of a “current” count value FRT val and of a “previous” countvalue, Prev FRT val.

In FIG. 4, reference 128 denotes a frequency change detection circuitwhich receives the signals FRT val and Prev FRT val as inputs andprovides a frequency change signal FC to the event counter 124 and tothe decoding unit or circuit 14.

In one or more embodiments a received frequency signal RF may besupplied to the bit decoding unit 14, e.g., in order to facilitatecertain decoding processes as discussed in the following.

In one or more embodiments the bit decoding unit 14 may provide feedbackto the processing unit 120 on the received (decoded) bits including,e.g., a signal RB and a signal irq to be discussed in the following.

In one or more embodiments, a change in frequency of the FSK-modulatedsignal (upper portion a) in FIG. 1) due to a change or transition in thelevel(s) of the modulating signal (lower portion b) in FIG. 1) can bedetected by considering a “window” including a number n of periods orcycles of the FSK-modulated signal FSK_(in).

In one or more embodiments, this may occur with a high sensitivity,namely with the capability of detecting even “thin” differences betweentwo received frequencies.

In one or more embodiments the number n of periods or cycles may berendered user-configurable (e.g., between 1 and 32), e.g., via thesignal WS as possibly provided by the processor 120 and configurationregister 122.

In one or more embodiments, during such a window two counts (see, e.g.,steps 1000 and 1002 in the flow chart of FIG. 6) may be performed by thecounter 126 under the control of the window counter 125.

During the first count (step 1000 in the flow chart of FIG. 6), the timeduration of a first set of n periods or cycles (that is the timeinterval required to receive n waveforms or pulses of the FSK-modulatedsignal) is determined.

During the second count (step 1002 in the flow chart of FIG. 6) the timeduration of a second, neighboring (e.g., subsequent) set of n subsequentperiods or cycles is determined.

The time duration/interval determined at each events gives an indicationof the (average) period of the FSK-modulated signal during thecorresponding window.

For instance, by assuming (for the sake of simplicity and ease ofunderstanding) that the frequency of the FSK-modulated signal changesfrom a frequency f1 to a frequency f0 due to the modulating signaltransitioning from “1” to “0” (see, e.g., FIG. 1) with—by way ofexample—f₁>f0:

-   -   the first count of n pulses (waveforms) will have a duration of        n times the period T1=1/f1 of the FSK-modulated waveform at the        first frequency f1;    -   the second count of n pulses (waveforms) will have a duration of        n times the period T0=1/f0 of the FSK-modulated wave form at the        second frequency f0.

The two signals FRT val and Prev FRT val (corresponding to thesubsequent counts 1000 and 1002 in the flow chart of FIG. 6) may then becompared in the frequency change detector 128 (step 1004 of the flowchart of FIG. 6) in order to ascertain whether the two counts are equalor differ.

If the two counts differ (e.g., more than certain sensitivity thresholdsuch as D in FIG. 2, which in the exemplary case considered in theforegoing may be due to a transition of the modulating signal from “1”to “0”) in a step 1006 a variation in the modulating signal will bedetected by the frequency change detector 128.

If, conversely, the two counts are equal (e.g., differ less than certainsensitivity threshold such as D in FIG. 2) in a step 1008 adetermination will be made that no changes/transitions have occurred inthe modulating signal (see for instance the situation depicted at thecenter of both portions a) and b) of FIG. 1) due, e.g., to the frequencyof the FSK-modulated signal remaining at the value f1 as a result of themodulating signal maintaining the “1” logical value.

The comparison between the two counts performed, e.g., in the frequencydetector 128 (step 1004 of the flow chart of FIG. 6) essentiallycorresponds to the basic concept represented in FIG. 2, that is:

-   -   no transition in the modulating signal is detected as long as        the changes/variations in the frequency of the FSK-modulated        signal remain within the Dzone (2×D) area.    -   a transition in the modulating signal is detected as a result of        a variation in the frequency of the FSK-modulated signal outside        the Dzone area.

Once frequency change detection (change/no change) has been effected insteps 1006 or 1008, operation may return “upstream” of the count steps1000, 1002 within the framework of a cyclical operation where the counts1000 and 1002 may correspond to a counting n periods or pulses of theFSK-modulated signal over two subsequent time windows or “events” whereone of the two counts (e.g., count 1000) is representative of a“previous” event—signal Prev FRT val—and the other count (e.g., count1002) is representative of a new, current count, with the “current”count at a certain event j becoming the “previous” count for asubsequent event j+1.

In one or more embodiments, any such count may provide an indication ofthe average period—thus frequency—of the FSK-modulated signal during acorresponding event or window.

Operation as exemplified in the foregoing is intrinsically robustagainst any drifts in the carrier of the FSK-signal, due to the“differential” nature of detection (wherein period/frequency over acertain time window is compared with the period/frequency over aprevious time window).

Also, the fact that each count gives an indication of an averageperiod/frequency of the FSK-signal over a certain time window makesoperation refractory to phase jumps as discussed in the introductoryportion to this description and to possible misalignment of the start ofthe counting windows with the frequency transitions produced by themodulating signal.

In one or more embodiments, frequency changes of the FSK-modulatedsignal may be detected by timing the period of the FSK_(in) signal bygrouping a number n of the FSK-modulated waveforms/pulses in a samemeasurement, with the possibility of achieving a high sensitivity evento small frequency changes.

The number n of pulses grouped in each window may be renderedconfigurable, e.g., via the signal WS from the unit 120, thus makingsuch sensitivity selectively adjustable.

For instance, in one or more embodiments as exemplified in FIG. 4 thewindow circuit 125 may be configured for receiving (e.g., from the unit120) a window size signal WS (e.g., n) with the capability ofenabling/disabling (start/stop signals) operation of the free runningcounter 126.

In one or more embodiments, the window circuit 125 may be configured forcounting the pulses of the FSK-modulated incoming signal FSK_(in) inorder to identify the end of a current window while the free runningcounter 126 may be configured simply as a free running timer to time theduration of a window of n periods by counting the pulses of the clocksignal clk fed thereto.

In one or more embodiments, the value reached by the free running timer126 at the end of each window may represent an estimation of the inputsignal frequency.

In one or more embodiments, the frequency change detector 128 may beconfigured in order to compare the signals FRT val and Prev FRT val foreach observation window to detect a frequency change, with thepossibility, if the input frequency does not change, that operation maycontinue until a time out occurs.

As a function of the time measured by the counter/timer 126, e.g., as aresult of the difference of the durations of two subsequent countwindows being higher or lower than a difference threshold correspondingto the width D of the Dzone 2×D of FIG. 2) a frequency change/nofrequency change condition may be detected and the respectiveinformation (signal FC) passed on to the bit decoding block 14.

One or more embodiments exemplified herein may thus operate by detectingfrequency changes by comparing a currently received frequency with apreviously received frequency and not, e.g., with a fixed calculatedthreshold.

As indicated, one or more embodiments may thus be insensitive tofrequency shifts/drifts in the FSK-carrier. By operating on “large”windows (that is with high values for n) the possibility exist ofdetecting even slight differences between frequencies (e.g., f0 and f1)with the capability of achieving a good degree of accuracy even when theexternal clock clk is not particularly fast.

In one or more embodiments, the width D of the 2×D Dzone area of FIG. 2may be programmable (e.g., via the unit 120) thus making it possible,e.g., for the user to “trim” the detector sensitivity, by taking intoaccount, e.g., operating conditions such as noise level and so on.

The exemplary presentation provided in the foregoing refers for the sakeof simplicity and ease of understanding the two-level FSK modulation(“0” and “1”), that is 2-FSK modulation of an FSK-modulated signal whichmay have two (nominal) frequencies f0 and f1.

As indicated, one or more embodiments may be applied to “multilevel”modulation. An exemplary case of such multilevel modulation may include,e.g., 4-FSK, that is an FSK-modulated signal which may have fourdifferent frequencies f0, f1, f2, f3 which may correspond to fourpossible bit combinations in a digital modulating signal, e.g., “00”,“01”, “10”, “11”. Extensions to higher levels such as 8-FSK, 16-FSK andso on are within the capability of the person skilled in the art.

In one or more embodiments as exemplified in FIG. 5, in addition to asignal (e.g., RF) indicative of a last measured frequency, the bitdecoding block 14 may receive as an input also information as to thetotal number of “samples” (e.g., the number of pulses/waveforms of theinput FSK-modulated signal) received at that frequency.

In one or more embodiments that information may be provided jointly bythe change frequency signal FC provided by the frequency change detector128 and the event number signal EN provided by the event counter 124 aspossibly processed in a length evaluation (sub)module or circuit 142.

In one or more embodiments the module or circuit 142 may be configuredin order to generate a length signal L which (e.g., in the case ofdecoding a Manchester-encoded signal) may be indicative of whether afrequency change occurred halfway of a transmitted bit, in order tounderstand if a “0” or a “1” was transmitted.

If a change (transition) occurs at an unexpected instant (e.g., due toan erroneous register configuration) and error signal LE (not visible inFIG. 4) may be activated and sent to the MPU unit 120

In that way, the FSK demodulator 10 may be configured for decoding thereceived bits by also taking into account specific modulation formats(e.g., Qi or PMA—these being just possible examples). Correspondinginformation (e.g., identifying a certain modulation format) may beprovided to the decoding block 14, e.g., on user controllable input 14a.

For instance, in the case of Qi, the time elapsed between two changes infrequency may play a role in demodulating the received signal which isencoded (in a manner known per se) according to a differential bi-phaseencoding scheme (e.g., with the two levels “0” and “1” represented bysignals exhibiting no transitions or a transition half-way the bitperiod).

One or more embodiments may also provide the capability of decodingsignals encoded with a Manchester code modulation scheme as may be thecase, e.g., of MA 1-8 communication protocol.

In one or more embodiments, an interrupt may be generated, e.g., as asignal irq from the bit decoding circuit 14 to the processing unit (MPU)120, e.g., when a certain bit is received.

For instance, the possibility may exist in one or more embodiments, of,e.g., using an internal buffer (such as the buffer 16 in FIG. 3) havinga length of, e.g., 32 bits, of concatenating subsequent bits, with thepossibility of configuring the number of bits which are accumulated inthe buffer before an interrupt.

In one or more embodiments, a further time-out interrupt can beprogrammed to interrupt (e.g., only) the unit 120 when the transmissionends and the receiving line returns to idle. This may permit receptionalso in the case the length of a transmitted packet is not known inadvance.

As indicated, one or more embodiments may be configured for reception ofsignals according to a Qi and/or a PMA protocol.

In the former case (Qi) a demodulator as the demodulator 10 of FIG. 3may be configured in order to:

-   -   detect the frequency variations in the FSK-modulated input        signal encoded with a by-phase coding,    -   decode the received bits thus detected,    -   receive a (programmed) number of bits and accumulate them within        an internal buffer 16,    -   interrupt the unit 120 (MPU) as a result of a desired number of        bits having been stored in the buffer or in the case such a        buffer is full.

In the case of PMA encoding (e.g., PMA Manchester encoding), aFSK-demodulator 10 as exemplified in FIG. 3 may be configured for:

-   -   demodulating the Manchester encoded signal as a function of the        frequency variations in the input signal detected, and    -   properly decoding Manchester-encoded received bits.

In one or more embodiments, a programmable time out feature as discussedin the foregoing may be provided (e.g., in the frequency changedetection module 128) when the line over which the FSK-modulated signalis received goes back to idle.

Such a feature may simplify an application software instruction code asused, e.g., for bit decoding.

One or more embodiments may provide a hardware implementation forFSK-demodulation including a frequency change detection module (e.g.,128) sensitive to “differential” changes in the frequency of theFSK-modulated signal (e.g., instead of the absolute values thereof).

One or more embodiments may provide a bit decoding module capable ofdemodulating bi-phase and/or Manchester code modulated signals.

One or more embodiments may include a programmable time out feature(e.g., at the FSK-change detection level) in order to detect when theline over which the FSK-modulated signal is received goes to idle.

One or more embodiments may provide a method of detecting aFSK-modulated waveform wherein the period of the FSK-modulated waveformvaries as a function of the level of a digital modulating signal (see,e.g., FIG. 1), the method including:

-   -   counting (e.g., at 1000 in FIG. 6) the occurrence of a first set        of n periods of the FSK-modulated waveform, said n periods of        said FSK-modulated waveform in said first set having a first        time duration,    -   counting (e.g., at 1002) the occurrence of a second set of n        periods of said FSK-modulated waveform, said n periods of said        FSK-modulated waveform in said second set having a second time        duration,    -   detecting and comparing (e.g., at 1004) said first time duration        and said second time duration, and    -   detecting (e.g., 1006) a change in the frequency (e.g., FC) of        said FSK-modulated waveform indicative of a change in the level        of said digital modulating signal as a result of said comparison        indicating a difference between said first time duration and        said second time duration reaching a detection threshold (D).

In one or more embodiments said first set of n periods and said secondset of n periods may be neighboring (e.g., subsequent) sets of periodsin said FSK-modulated waveform.

One or more embodiments may include cyclically counting (e.g., at 1000,1002) the occurrence of sets of n periods of said FSK-modulated waveformover subsequent time windows (see, e.g., the window counter circuit 125and the counter 126) wherein:

-   -   said first set of n periods includes a set of n periods of said        FSK-modulated waveform during a current time window (e.g., FRT        val), and    -   said second set of n periods includes a set of n periods of said        FSK-modulated waveform during a previous time window (e.g., Prev        FRT val).

One or more embodiments may include making said number n of periods ofsaid FSK-modulated waveform selectively adjustable (e.g., at 120).

One or more embodiments may include making said difference threshold(e.g., D in FIG. 2) selectively adjustable (e.g., at 120).

One or more embodiments may include recovering said digital modulatingsignal (e.g., at the bit decoding block 14) as a function of the changesin the frequency of said FSK-modulated waveform detected as a result ofsaid comparison (e.g., 1004 in FIG. 6).

One or more embodiments may include buffering (e.g., at 16) theinformation bits conveyed by said recovered digital modulating signal.

One or more embodiments may include generating interrupt signals (e.g.,irq) for at least partly discontinuing detection (e.g., by interruptingthe unit 120) as a result of, e.g., any of:

-   -   reception of said FSK-modulated waveform being discontinued,        and/or    -   the number of said buffered bits reaching a threshold value,        and/or    -   the buffered bits having filled a respective buffer.

One or more embodiments may relate to a circuit (e.g., 12) including:

-   -   counting circuitry (e.g., 125, 126) configured for counting the        occurrence of sets of n periods in a FSK-modulated waveform,        wherein the period of said FSK-modulated waveform varies as a        function of the level of a digital modulating signal, the        counting circuitry configured to:        -   i) counting (e.g., 1000) the occurrence of a first set of n            periods of said FSK-modulated waveform, said n periods of            said FSK-modulated waveform in said first set having a first            time duration,        -   ii) count (e.g., 1002) the occurrence of a second set of n            periods of said FSK-modulated waveform, said n periods of            said FSK-modulated waveform in said second set having a            second time duration,    -   a frequency change detection module (e.g., 128) coupled with        said counting circuitry to receive therefrom at least one signal        (e.g., FRT val, Prev FRT val) indicative of said first time        duration and said second time duration, comparing (e.g., 1004)        said first time duration and said second time duration and        generating at least one detection signal (e.g., FC) indicative        of the occurrence of variations in the frequency of said        FSK-modulated waveform as a result of the difference between        said first time duration and said second time duration reaching        a detection threshold (e.g., D), wherein the circuit is        configured for implementing the method of one or more        embodiments.

One or more embodiments may relate to an FSK-demodulator (e.g., 10)including:

-   -   a circuit (e.g., 12) according to one or more embodiments, and    -   a bit decoding module (e.g., 14) coupled with said circuit to        receive therefrom said at least one detection signal indicative        of the occurrence of variations in the frequency of said        FSK-modulated waveform, the bit decoding module configured for        recovering from said at least one detection signal the        information bits conveyed by said digital modulating signal.

One or more embodiments may include a buffer module (e.g., 16) forstoring a plurality of information bits conveyed by said digitalmodulating signal recovered from said at least one detection signal.

On one or more embodiments said decoding module may be configured fordecoding at least one of a differential by-phase encoded signal and aManchester-encoded signal.

One or more embodiments may relate to a computer program product,loadable in the memory of at least one processing device and includingsoftware code portions for performing the method of one or moreembodiments.

Without prejudice to the underlying principles, the details andembodiments may vary, even significantly, with respect to what has beendescribed in the foregoing by way of example only, without departingfrom the extent of protection.

Some embodiments may take the form of or include computer programproducts. For example, according to one embodiment there is provided acomputer readable medium including a computer program adapted to performone or more of the methods or functions described above. The medium maybe a physical storage medium such as for example a Read Only Memory(ROM) chip, or a disk such as a Digital Versatile Disk (DVD-ROM),Compact Disk (CD-ROM), a hard disk, a memory, a network, or a portablemedia article to be read by an appropriate drive or via an appropriateconnection, including as encoded in one or more barcodes or otherrelated codes stored on one or more such computer-readable mediums andbeing readable by an appropriate reader device.

Furthermore, in some embodiments, some of the systems and/or modulesand/or circuits and/or blocks may be implemented or provided in othermanners, such as at least partially in firmware and/or hardware,including, but not limited to, one or more application-specificintegrated circuits (ASICs), digital signal processors, discretecircuitry, logic gates, standard integrated circuits, state machines,look-up tables, controllers (e.g., by executing appropriateinstructions, and including microcontrollers and/or embeddedcontrollers), field-programmable gate arrays (FPGAs), complexprogrammable logic devices (CPLDs), etc., as well as devices that employRFID technology, and various combinations thereof.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A method, comprising: counting anoccurrence of a first set of n periods of a frequency-shift-keying(FSK)-modulated waveform, where n is an integer number, said n periodsof said FSK-modulated waveform in said first set having a first timeduration, wherein a period of the FSK-modulated waveform varies as afunction of a level of a digital modulation signal; counting anoccurrence of a second set of n periods of said FSK-modulated waveform,said n periods of said FSK-modulated waveform in said second set havinga second time duration; determining, based on the counting of the firstset of n periods, the first time duration; determining, based on thecounting of the second set of n periods, the second time duration;comparing a difference between said first time duration and said secondtime duration to a threshold; and detecting a change in a frequency ofsaid FSK-modulated waveform indicative of a change in the level of saiddigital modulating signal based on the comparing of the differencebetween the first time duration and the second time duration to thethreshold, wherein: the method comprises cyclically counting occurrencesof sets of n periods of said FSK-modulated waveform over sequential timewindows, said first set of n periods includes a set of n periods of saidFSK-modulated waveform during a current time window, and said second setof n periods includes a set of n periods of said FSK-modulated waveformduring a previous time window.
 2. The method of claim 1 wherein saidfirst set of n periods and said second set of n periods are neighboringsets of periods in said FSK-modulated waveform.
 3. A method, comprising:counting an occurrence of a first set of n periods of afrequency-shift-keying (FSK)-modulated waveform, where n is an integernumber, said n periods of said FSK-modulated waveform in said first sethaving a first time duration, wherein a period of the FSK-modulatedwaveform varies as a function of a level of a digital modulation signal;counting an occurrence of a second set of n periods of saidFSK-modulated waveform, said n periods of said FSK-modulated waveform insaid second set having a second time duration; determining, based on thecounting of the first set of n periods, the first time duration;determining, based on the counting of the second set of n periods, thesecond time duration; comparing a difference between said first timeduration and said second time duration to a threshold; and detecting achange in a frequency of said FSK-modulated waveform indicative of achange in the level of said digital modulating signal based on thecomparing of the difference between the first time duration and thesecond time duration to the threshold, wherein the method comprises:recovering said digital modulation signal as a function of detectedchanges in the frequency of said FSK-modulated waveform based on aseries of comparisons of differences between durations of sets of nperiods to the threshold; detecting a discontinuation of reception ofthe FSK-modulated waveform; and generating an interrupt signal inresponse to the detection of the discontinuation.
 4. The method of claim3, comprising: cyclically counting occurrences of sets of n periods ofsaid FSK-modulated waveform over sequential time windows wherein: saidfirst set of n periods includes a set of n periods of said FSK-modulatedwaveform during a current time window, and said second set of n periodsincludes a set of n periods of said FSK-modulated waveform during aprevious time window.
 5. The method of claim 1, comprising: adjustingsaid number n of periods of said FSK-modulated waveform.
 6. The methodof claim 1, comprising: adjusting said threshold.
 7. The method of claim1, comprising: recovering said digital modulation signal as a functionof detected changes in the frequency of said FSK-modulated waveformbased on a series of comparisons of differences between durations ofsets of n periods to the threshold.
 8. The method of claim 7,comprising: buffering information bits of said recovered digitalmodulation signal.
 9. A method, comprising: counting an occurrence of afirst set of n periods of a frequency-shift-keying (FSK)-modulatedwaveform, where n is an integer number, said n periods of saidFSK-modulated waveform in said first set having a first time duration,wherein a period of the FSK-modulated waveform varies as a function of alevel of a digital modulation signal; counting an occurrence of a secondset of n periods of said FSK-modulated waveform, said n periods of saidFSK-modulated waveform in said second set having a second time duration;determining, based on the counting of the first set of n periods, thefirst time duration; determining, based on the counting of the secondset of n periods, the second time duration; comparing a differencebetween said first time duration and said second time duration to athreshold; and detecting a change in a frequency of said FSK-modulatedwaveform indicative of a change in the level of said digital modulatingsignal based on the comparing of the difference between the first timeduration and the second time duration to the threshold, wherein themethod comprises: recovering said digital modulation signal as afunction of detected changes in the frequency of said FSK-modulatedwaveform based on a series of comparisons of differences betweendurations of sets of n periods to the threshold; buffering informationbits of said recovered digital modulation signal; and generating aninterrupt signal in response to at least one of: a number of saidbuffered bits reaching a threshold number of bits; and a bufferoverflow.
 10. A device, comprising: one or more memories; andfrequency-shift detection circuitry, which, in operation: countsoccurrences of sets of n periods of a received frequency-shift-keying(FSK)-modulated waveform, where n is an integer number; determines,based on the counting, time durations corresponding to respective setsof n periods; compares differences between time durations correspondingto respective sets of n periods to a threshold difference; and generatesone or more signals indicative of variations in frequency of theFSK-modulated waveform based on the comparing of the differences betweentime durations to the threshold difference, wherein the frequency-shiftdetecting circuitry, in operation: cyclically counts occurrences of setsof n periods of said FSK-modulated waveform over sequential time windowswherein: a first set of n periods includes a set of n periods of saidFSK-modulated waveform during a current time window; a second set of nperiods includes a set of n periods of said FSK-modulated waveformduring a previous time window; and a difference between a time durationcorresponding to the first set of n periods and a time durationcorresponding to the second set of n periods is compared to thethreshold difference.
 11. The device of claim 10 wherein thefrequency-shift detecting circuitry, in operation, compares differencesbetween time durations of neighboring sets of n periods in saidFSK-modulated waveform to the threshold difference.
 12. A device,comprising: one or more memories; and frequency-shift detectioncircuitry, which, in operation: counts occurrences of sets of n periodsof a received frequency-shift-keying (FSK)-modulated waveform, where nis an integer number; determines, based on the counting, time durationscorresponding to respective sets of n periods; compares differencesbetween time durations corresponding to respective sets of n periods toa threshold difference; and generates one or more signals indicative ofvariations in frequency of the FSK-modulated waveform based on thecomparing of the differences between time durations to the thresholddifference, wherein the frequency-shift detecting circuitry, inoperation: detects discontinuations of reception of the FSK-modulatedwaveform; and generates an interrupt signal in response to detection ofa discontinuation.
 13. The device of claim 12 wherein thefrequency-shift detecting circuitry, in operation: cyclically countsoccurrences of sets of n periods of said FSK-modulated waveform oversequential time windows wherein: a first set of n periods includes a setof n periods of said FSK-modulated waveform during a current timewindow; a second set of n periods includes a set of n periods of saidFSK-modulated waveform during a previous time window; and a differencebetween a time duration corresponding to the first set of n periods anda time duration corresponding to the second set of n periods is comparedto the threshold difference.
 14. The device of claim 10 wherein n isadjustable.
 15. The device of claim 10 wherein the threshold differenceis adjustable.
 16. The device of claim 10, comprising: decodingcircuitry, which, in operation, recovers a digital modulation signalbased on the one or more signals indicative of variations in frequencyof the FSK-modulated waveform generated in response to a series ofcomparisons of differences between durations corresponding to sets of nperiods to the threshold difference.
 17. The device of claim 10, whereinthe frequency-shift detecting circuitry, in operation, recovers adigital modulation signal based on the one or more signals indicative ofvariations in frequency of the FSK-modulated waveform generated inresponse to a series of comparisons of differences between durationscorresponding to sets of n periods to the threshold difference.
 18. Thedevice of claim 17 wherein the one or more memories comprise a buffer,which, in operation, buffers information bits of said recovered digitalmodulation signal.
 19. The device of claim 18 wherein thefrequency-shift detecting circuitry, in operation, generates aninterrupt signal in response to at least one of: a number of saidbuffered bits reaching a threshold number of bits; and a bufferoverflow.
 20. A system, comprising: receiving circuitry, which, inoperation: counts occurrences of sets of n periods of a receivedfrequency-shift-keying (FSK)-modulated waveform, where n is an integernumber; determines, based on the counting, time durations correspondingto respective sets of n periods; compares differences between timedurations corresponding to respective sets of n periods to a thresholddifference; and generates one or more signals indicative of variationsin frequency of the FSK-modulated waveform based on the comparing of thedifferences between time durations to the threshold difference; anddecoding circuitry, which, in operation, recovers a digital modulationsignal based on the one or more signals indicative of variations infrequency of the FSK-modulated waveform generated in response to aseries of comparisons of differences between durations corresponding tosets of n periods to the threshold difference, wherein the decodingcircuitry, in operation, decodes at least one of a differential by-phaseencoded signal and a Manchester-encoded signal.
 21. The system of claim20, including a buffer, which, in operation, stores information bits ofthe recovered digital modulation signal.
 22. A system, comprising:receiving circuitry, which, in operation: counts occurrences of sets ofn periods of a received frequency-shift-keying (FSK)-modulated waveform,where n is an integer number; determines, based on the counting, timedurations corresponding to respective sets of n periods; comparesdifferences between time durations corresponding to respective sets of nperiods to a threshold difference; and generates one or more signalsindicative of variations in frequency of the FSK-modulated waveformbased on the comparing of the differences between time durations to thethreshold difference; decoding circuitry, which, in operation, recoversa digital modulation signal based on the one or more signals indicativeof variations in frequency of the FSK-modulated waveform generated inresponse to a series of comparisons of differences between durationscorresponding to sets of n periods to the threshold difference; andpower control circuitry, which, in operation, controls a chargingprocess based on the recovered digital modulation signal.
 23. The systemof claim 22 wherein the decoding circuitry, in operation, decodes atleast one of a differential by-phase encoded signal and aManchester-encoded signal.
 24. A non-transitory, computer-readablemedium having contents which cause a signal processing circuit toperform a method, the method comprising: counting occurrences of sets ofn periods of a received frequency-shift-keying (FSK)-modulated waveform,where n is an integer number; determining, based on the counting, timedurations corresponding to respective sets of n periods; comparingdifferences between time durations corresponding to respective sets of nperiods to a threshold difference; generating one or more signalsindicative of variations in frequency of the FSK-modulated waveformbased on the comparing of the differences between time durations to thethreshold difference; recovering a digital modulation signal based onthe one or more signals indicative of variations in frequency of theFSK-modulated waveform generated in response to a series of comparisonsof differences between durations corresponding to sets of n periods tothe threshold difference; and controlling a charging process based onthe recovered digital modulation signal.
 25. The non-transitory,computer-readable medium of claim 24 wherein the signal processingcircuit comprises one or more memories and one or more processing cores.26. A non-transitory, computer-readable medium having contents whichcause a signal processing circuit to perform a method, the methodcomprising: counting an occurrence of a first set of n periods of afrequency-shift-keying (FSK)-modulated waveform, where n is an integernumber, said n periods of said FSK-modulated waveform in said first sethaving a first time duration, wherein a period of the FSK-modulatedwaveform varies as a function of a level of a digital modulation signal;counting an occurrence of a second set of n periods of saidFSK-modulated waveform, said n periods of said FSK-modulated waveform insaid second set having a second time duration; determining, based on thecounting of the first set of n periods, the first time duration;determining, based on the counting of the second set of n periods, thesecond time duration; comparing a difference between said first timeduration and said second time duration to a threshold; and detecting achange in a frequency of said FSK-modulated waveform indicative of achange in the level of said digital modulating signal based on thecomparing of the difference between the first time duration and thesecond time duration to the threshold, wherein: the method comprisescyclically counting occurrences of sets of n periods of saidFSK-modulated waveform over sequential time windows, said first set of nperiods includes a set of n periods of said FSK-modulated waveformduring a current time window, and said second set of n periods includesa set of n periods of said FSK-modulated waveform during a previous timewindow.